It should be simple to construct that aerial. You need ~1.2m of 9.5mm aluminium tube from Metal Centre (see above). Cut the tube into 9 pieces using a Junior hacksaw (very small one) with the following lengths (in mm) - 168, 77, 77, 140, 136, 136, 130, 128, 126. If you cut the pieces 1-2mm longer than necessary you can file them down to the correct length with a sandpaper block so they have smooth square edges.
Next you need an ~1m boom to mount them on. The only purpose of the boom is to hold the small pieces of tube in place in the correct positions. You could use one of those square wooden stakes that they sell at the nurseries to support growing plants (~R5) or a wooden dowel stick from a hardware store. A nursery stake may be more durable when exposed to the rain etc. If you have a 1m piece of white plastic conduit available then this will also be suitable. You will probably need to purchase caps for both ends if you use a conduit to seal it to prevent it filling up with water when it rains. You can either drill 9.5mm holes through the centre of the boom and push the aluminium tubes through the holes or you can just glue the aluminium tubes onto the surface of the boom with epoxy or Q-bond (in this case a square wooden nursery stake would be preferable). You probably need to attach the boom to a TV aerial mast so you must leave some space on the boom for this purpose. Make a mark about 20cm from one end of the boom for the reflector (168mm piece of tube). From this point make markings at 74, 124, 202, 314, 428, 549 and 670mm. If you have done everything correctly the last mark should be 130mm away from the other end of the boom. These are the positions where you need to either drill holes or just glue the pieces of tube in place. All of the pieces must lie exactly parallel to each other as you can see in the photo of the aerial from your link. The driven element consists of two pieces of tube 77mm each in length. You need to find a small piece of wooden rod that you can squeeze inside both of the two tubes to keep them separated from one another by a distance of 1mm. The two wires of the coaxial cable need to be attached to the two pieces of the driven element. You can either use small screws with internal nuts or possibly very small fuel hose clips (jubilee clips) that you can tighten to hold the wires firmly against the aluminium tubes. Something like this would probably be suitable (the smaller the better and cut off any protruding strap) -
http://www.sidewindercomputers.com/brmihocl7int.html
The screen and the central conductor wire must be kept very short. The cable will probably be the most expensive item. You can either purchase RG-58/U which is the cheapest option or LMR195 (slightly more expensive) or LMR400 (quite expensive) depending on your signal strength. The cheaper cables degrade the signal more than the more expensive ones. If your signal is very marginal then you may find that a better quality cable helps although I would recommend either the RG-58/U or the LMR195 at first. If you are using a wooden boom you should give it several coats of varnish after the glue has dried. Don't varnish the aluminium pipes, just the boom as this may affect the performance very slightly.
Here are links to suppliers for the different types of cables/connectors. You should first phone some of the electronic component suppliers in your area to enquire as the petrol charges could be higher than any component savings. You could ask the shop about attaching the N-connector to one side of the cable when you purchase it if you don't think that you will be able to attach this yourself. Make sure that you measure the amount of cable that you require very carefully before purchasing it using a piece of string as you can't join on additional pieces once it has been cut. It is also quite expensive so you don't want to purchase much more than is required.
N-type connectors and coaxial cables
http://www.mantech.co.za/Stock.aspx?Query=N-typeand
http://www.rfdesign.co.za/pages/5645456/Products/RF-Cables/RF-Cables.asp
http://www.rfdesign.co.za/pages/5645456/Products/RF-Connectors/N-TYPE-connectors.asp
Alternative sources for N-type connectors and coaxial cables (possibly more convenient - phone to enquire first)
www.mantech.co.za
www.spectron.co.za
www.spacetv.co.za
www.communica.co.za
www.ellies.co.za
www.zakspeed.co.za
www.miro.co.za
To summarise the costs - aluminium tube (~R14 for 2m), wooden boom or 1m piece of conduit (~R5), N-connector (~R25) and then RG158/U or LMR195 (~R5-R10 per metre).
